I'm sure I'm going to catch a lot of flak for this one;

The Lord of the Rings series.

I tried reading these when I was younger and was bored out of my head when Tom Bomdabom (whatever) showed up. All the "songs" that they sang in it were boring as hell too.

I tried again when I saw the first movie and was all "Jaysus these are boring".

But I'm sure that there are plenty other movies that were better than the books they were based upon.